Glauconite and Phosphate Peloids in Mesozoic Carbonate Sediments (Eastern Subbetic Zone, Betic Cordilleras, SE Spain)

Abstract

Glauconite and Ca phosphate peloids occur in Jurassic and Cretaceous bioclastic carbonate rocks from pelagic swell sequences of the Algayat-Crevillente Unit (Subbetic Zone). The size and morphology of the peloids are controlled by the bioclasts. The glauconite in both stratigraphic positions is K rich (>0.69 atoms p.f.u.) and shows well-defined 10 A. lattice fringes. Poorly crystalline areas with a composition of Fe-smectite are found within the peloids, indicating the nature of the glauconitic precursor. This precursor would be formed in the shielded microenvironments of the bioclast and later transformed to glauconite by equilibration of peloids with sea water that culminated with the crystallization of a phosphatic phase. The greater presence of smectite areas in the Jurassic peloids and the lower K contents (0.69-0.81) of these glauconites, compared with the Cretaceous glauconites (0.81-0.89) can be explained by the calcitic early diagenetic cementation which stopped the process of glauconitization.

Reappraisal of the GL‐O Reference Material for K‐Ar Dating: New Insight from Microanalysis, Single‐Grain and Milligram Ar Measurements

“…The coexistence of glauconite and phosphates in various marine formations has been described previously (Birch , Brasier , Odin and Letolle , O’Brien et al , Carson and Crawley , Stille and Clauer , Jiménez‐Millán et al , Wigley and Compton ).…”

Paleoenvironmental Conditions during the Paleocene–Eocene Transition Imprinted within the Glauconitic Giral Member of the Barmer Basin, India

“…The basal (001) reflection of glauconite appears within 10 Å and 14 Å. The ordered glauconite has a 10 Å basal spacing while the smectite minerals exhibit 14 Å basal spacing [1,[12][13][14][15]43]. The basal reflection of the (001) plane at 11.89 Å in air-dried Giral samples expands upon glycolation, indicating considerable smectite interstratification within glauconite [44].…”

“…Glauconite occurs as rounded to sub-rounded, light-green to dark-green pellets that form on the sediment-seawater interface [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The evolution of early formed glauconite leads to widely varying compositional range from an interlayer-deficient, K-poor glauconitic smectite to K-rich glauconitic mica [1], within which the interlayer Na content rarely exceeds 1 wt%.…”

Water–Rock Interaction Processes in Tíscar and Larva Active Faults (Betic Cordillera, SE Spain)

“…In fault zones, the reason why a mineral assemblage crystallizes depends not only on the temperature but also on the elemental composition of the fluids reacting with the protolith and the crystallization mechanism [50,51]. Clay minerals can replace previous minerals or can be formed by direct precipitation from fluids circulating in the area [52,53]. The concentration and circulation of fluids in the microstructures of fault rocks, even under very low temperatures, can promote the neoformation of clays by processes of structural diagenesis [7,54].…”